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Is your new solar system producing the power output it should ?

A very common question I get from people who have just got a new solar power system is: “Now the solar panels are on my roof, how do I know what the solar system output should be ? ”.

The solar power system owners are usually a bit concerned because they have bought, for example, a  5kW system but their inverter is telling them that they only got 4kW of peak power  yesterday! Where's the missing 1kW ? Most people expect a 5kW solar system output !

A fact that isn't advertised widely in the solar industry is that most solar systems in China conditions will usually peak at only 80% of their specified peak power.

This is actually completely normal in almost any industry that sells hardware that has associated specs. Think about the last time you bought a car with a specified fuel consumption from the manufacturer. Did your car actually ever achieve that fuel efficiency on a day-to-day basis ? Thought not !

Solar panel systems usually reach only 80% of their specified peak due to “system losses“. So what are these system losses, and how can you work them out for the solar power system sitting on your roof ?

The 5 Losses In Every Solar Power System

1. Manufacturer's power tolerance.  (1%)

All panels have a power tolerance , is about -1%/+3%. So worst case is that the specified power output is actually 1% lower than spec.

2. Temperature Loss. (10%)

Most solar panels lose about 10% of their rated power on a 25°C day, more if it is hotter. Let's assume 10% for this estimate.

3. Dirt (5%)

When your solar panels are put on your roof, airborne particulates like dust will settle on the panels' glass. These particulates block the amount of sunlight reaching the solar cells behind the glass reducing your power. The reduction in power from particulate build up typically lies in the 5%-15% range. 

4. Wiring Losses (voltage drops) (2%)

All the solar panels on your roof are interconnected with wires, then a long pair of DC wires connects the final solar panel to your inverter. All these wires have a small electrical resistance, which means the electricity flowing through them will suffer a voltage drop. This will reduce your power proportionally, typically by around 2%.

5. Inverter Efficiency (4%)

Everything goes through your inverter so the inverter efficiency will directly affect your system output. An inverter efficiency of about 96% , giving a 4% loss.

Multiply all those together ( see the pic on the right )  and you are looking at 20% total losses, giving a real world peak power of 4kW.

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